This invention relates generally to turbine engines and, more particularly, to variable vane assemblies within a turbine engine.
Gas turbine engines generally include a high pressure compressor for compressing air flowing through the engine, a combustor in which fuel is mixed with the compressed air and ignited to form a high energy gas stream, and a high pressure turbine. The high pressure compressor, combustor, and high pressure turbine sometimes are collectively referred to as the core engine. Such gas turbine engines also may include a low pressure compressor for supplying compressed air, for further compression, to the high pressure compressor, and a fan for supplying air to the low pressure compressor.
The high pressure compressor typically includes a rotor surrounded by a casing. The casing is typically fabricated to be removable, such as by forming the casing into two halves that are then removably joined together. The high pressure compressor includes a plurality of stages and each stage includes a row of rotor blades and a row of stator vanes. The casing supports the stator vanes, and the rotor supports the rotor blades. The stator vane rows are between the rotor blade rows and direct air flow into a downstream rotor blade row.
Variable stator vane assemblies are utilized to control the amount of air flowing through the compressor to optimize performance of the compressor. Each variable stator vane assembly includes a variable stator vane which extends between adjacent rotor blades and the variable stator vane is rotatable about an axis. The orientation of the variable stator vane affects air flow through the compressor.
In a known variable vane assembly, a trunnion bushing is positioned around a portion of a variable vane so that the variable vane extends through the trunnion bushing. The assembly is bolted onto the high pressure compressor stator casing with the trunnion bushing between the variable vane and the casing. Such assemblies have possible gas leakage paths, such as between an outside diameter of the airfoil and an inside diameter of the bushing. In addition, another leakage path is between an outside diameter of the bushing and an inside diameter of the compressor stator case opening. Such leakage may result in failure of the bushing due to oxidation and erosion caused by the high velocity high temperature air. Once the bushing fails, an increase in leakage past the stator vane occurs, which results in a performance loss. In addition, the loss of the bushing allows contact between the vane and the casing which causes wear and increases the engine overhaul costs.
Accordingly, it would be desirable to provide a variable vane assembly that reduces, or eliminates, leakage of air through the casing. In addition, it would be desirable to provide such an assembly which is relatively inexpensive and simple to install.